<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
  <!--   <input type="text" id='a1' value=''>
    <button id="b1">提交</button>
    <script>
         var a=document.getElementById('a1')
         var b=document.getElementById('b1')
        //  console.log(a);
      /*   console.log(a.value);
        console.log(b); */
    b.onclick=function(){
        // console.log(112);
        var num=parseInt(a.value)
        if(num<60 && num>=0){
            alert('不及格')
    }else if(num<70 && num>=60){
        alert('及格')
    }else if(num<80 && num>=70){
        alert("棒")
    }else{
        alert('唱过')
    }

    }

    </script> -->
    <input type="text" id="a">
    <select name="" id="c">
        <option value="+">+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>

    </select>
    <input type="text" id="b">
    <button id="d">点击</button>
    结果：<input type="text" id="jg">
    <script>
        var dj=document.getElementById('d')
        var a_=document.getElementById('a')
        var b_=document.getElementById('b')
        var select=document.getElementById('c')
        dj.onclick=function(){
           /*  console.log(111);
        console.log(222); */
        }
       /*  console.log(111);
        console.log(222); */
        var a=parseInt(a_.value)
        var b=parseInt(b_.value)
        // console.log(a,b);
    </script>
   
</body>
</html>